1. Field of the Invention
The present invention relates to the exercise of control over a multi-stage drawing machine and, particularly, a machine which performs a direct, non-slip drawing of elongated stock material to form such material into a desired shape. More specifically, this invention is directed to the automatic set-up and subsequent control over the individual drives of a cascaded drawing system wherein stock material is serially pulled through a plurality of stationary dies. Accordingly, the general objects of the present invention are to provide novel and improved methods of such character.
2. Description of the Prior Art
Drawing systems for forming, from elongated stock typically fed from a supply reel, products having a desired cross-sectional size and shape are well known in the art. Such systems are commonly used to produce wire, endless strips and endless sections by a direct, non-slip, straight process without the intervention of cutting tools. The prior art drawing systems are provided with plural drives. These individual drives are typically located immediately downstream of an associated die and are independently adjustable to control the interrelated drawing process parameters of the speed of the stock material relative to the die and the force applied to pull the material through the die. These controllable process parameters will be adjusted, as a function of the forming process, to ensure that there will be no slippage of the stock material relative to the dies. As a practical matter, the process variables cannot be predetermined and set because the coaction of each individual die with the stock material will be different. These differences, i.e., the process dependencies, can result in the stock material being damaged or destroyed by, for example, being overstressed or being advanced to one of the cascaded dies too rapidly.
As a consequence of the operating difficulty briefly discussed above, conventional prior practice has been to have skilled operating personnel exercise manual control over the process variables. A drawing process wherein such manual control is exercised is described in German Patent 27 49 505. It has also been proposed to employ semi-automatic control employing relatively costly apparatus with control rollers such as, for example, described in German Patent 1 072 216. An alternative automatic control, wherein contact rollers are employed to sense the operating conditions intermediate the individual dies, is described in published German Patent Application 30 09 779. A further prior art approach to the exercise of control over a multiple die drawing machine, wherein the force on the individual die holders is measured, is described in published German Patent Application 2 140 580. Finally, in the proposed control process described in published German Application 40 09 732, sensors comprising rollers which are in contact with the stock material are used during the set-up and are retracted during continuous operation.
All of the above briefly described examples of prior art drawing machine control processes and apparatus share a common deficiency. Specifically, the productivity of the systems and the quality of the final product are highly dependent upon the experience and skill of the operating personnel. A further disadvantage of most of the prior art techniques which seek to obtain a degree of automation resides in the added cost and reduced system reliability incident to the use of contact rollers or other sensors which contact the stock material. The lack of reliability results from the inherent wear of the contact rollers. A further disadvantage incident to the use of contact rollers is that they necessarily reduce processing speed through tending to cause the stock material to be misaligned with the inlets of the drawing dies. Indeed, with some materials or sections, the added bending of the stock material resulting from the use of contact rollers cannot be tolerated because of the deleterious effect on the quality of the end product.
To summarize, there has been a long standing desire in the art to exercise automatic control over a multiple die drawing machine that implements a direct, non-slip drawing process. The desired automatic control would exercise supervision over the individual drives associated with each drawing die to ensure that the load imposed on the stock material and its speed would be adjusted to values commensurate with the instantaneous material properties as well as to values commensurate with conditions at the upstream and downstream dies. A control of the type long desired would determine the actual instantaneous parameters without the use of force measurement devices or other stock material contacting devices such as, for example, compensation rollers and contact rollers.